www.sinclairintl.com/cgi-bin/category.cgi?category=search&item=LAP-1&type=store
"If all bases, rings, and actions were manufactured in perfect sync with each other, mounting a scope would be a piece of cake. Whether you use a one-piece base or two-piece base, the odds are generally against you that they will be in perfect alignment. If you ignore this status and tightened your new $800.00 scope in your misaligned rings, the result is that you will cause the scope tube to actually bend to match the misalignment of the scope rings. This will put the inner workings of the scope in a bind. Our lapping tool will help alleviate this problem.
The lapping tool consist of a steel bar of correct dimension to fit your rings, a handle and some lapping compound (enough to do about 5 sets of rings). This tool is used to remove metal from the scope rings where it is causing the tube deflection. This procedure actually puts the bearing surface of each ring in alignment with the other.
When a new scope leaves the factory it is optically centered. Problems with alignment that are not corrected require you to adjust the scope using the elevation and/or windage knobs. Excessive movement may cause the image to be distorted or create a negative parallax condition. Extreme amounts of adjustment to correct or misaligned rings and bases also tend to hamper the scope’s light gathering qualities, thus making the sight picture darker.
The other thing to look for on your bases is to watch for clearance underneath. If your base is not fitted perfectly flush to the receiver you may want to think about shimming the base to allow it to seat properly. We recommend two-piece bases in most applications. Some people argue that a one-piece base adds strength to the action. Do you really think a 5” long piece of thin aluminum or steel is going to provide much strength to an action?
The Sinclair lapping tool takes a little bit of elbow grease but is a relatively simple procedure to perform and we provide plenty of good instructions."
They also make a 30mm tool. John